Photovoltaic cells are semiconductor devices that directly convert incident light from the ultra-violet through the infrared into electricity via the photovoltaic effect. Solar cells are a particular category of photovoltaic cells that are utilized to convert sunlight into electricity. In a typical solar energy application, a plurality of solar cells—usually hundreds or thousands—are combined into a single structural and electrical unit known as a solar panel, or more generally, a photovoltaic module.
A photovoltaic module employed for solar power generation is typically of the order of 3 feet×5 feet×1 inch (1 m×1.5 m×0.025 m) in size, although in principle it can be any size consistent with safe handling and electrical safety of the installed system. Normally a solar energy installation will constitute a photovoltaic array that includes a plurality of such modules, from perhaps 25 on a residential roof to hundreds or even thousands for major power installations. The output from a single module made up of polycrystalline silicon photocells is 4-5 amperes of direct current at a voltage of 24 volts.
A significant reflectance loss occurs at the front surface of a glass front sheet of a solar panel. Cumulative (i.e., in a full day) reflectance loss of as much as 4-10% may result due to angle of incidence effects. Increasing the amount of incident light transmitted through the glass to the photovoltaic cells beneath can increase the energy output from the solar panel. Even small percentage changes are considered significant in the solar energy industry.
It is known in the art to employ so-called anti-reflection (AR) coatings on reflective substrates in order to reduce the intensity of reflected light.
Copending applications 61/015,069, 61/015,074, 61/015,080, and 61/015,063 disclose various aspects of an antireflection coating comprising two layers, each layer comprising a fluoropolymer, particularly a fluoroelastomer, and wherein one layer further comprises nano-scale inorganic particles (nanoparticles), the layer containing nanoparticles being characterized as having a higher refractive index than the layer not containing nano-particles. Further disclosed therein is an antireflection coating disposed upon various non-fluorinated organic polymeric substrates as well as glass.
U.S. Pat. No. 6,680,080 discloses deposition of single layer fluoropolymer film by solution deposition onto soda-lime glass, and phosphate glasses in particular. Teflon® copolymers are recited.
Patent applications assigned to the 3M company (US2007/0286994, US2007/0285778, and US2006/0275627) disclose bi-layer AR films having a low refractive index comprising a fluorinated material and a high refractive index layer comprising nano-scale inorganic particles. The high refractive index layer does not comprise a fluorinated material. Deposition on glass is disclosed.
JP1991266801(A) discloses a multi-layer fluoropolymeric structure employed as an AR coating. The multi-layer coating disclosed is an inorganic dielectric film antireflection coating disposed upon a reflective substrate such as glass. Disposed upon the inorganic dielectric film is a fluoropolymer film 3—100 nanometers (nm) in thickness. Further disclosed is an antireflective film created on the surface of a base material that consists of a single- or multi-layered inorganic dielectric thin film. When it is a single layer, it is made from a material which has a lower refractive index (normally η is 1.3-1.5) than the base material. In the case of two layers, a material with a higher refractive index (normally η is 1.9-2.4) is next to the base material, followed by a material with a lower refractive index. When it is three-layered, a material with a medium refractive index (normally η is 1.5-1.9) is next to the base material, followed by a material with a high refractive index, and then a material with a low refractive index. The thicknesses of each inorganic dielectric thin film layer is disclosed to be (where λ is a design wavelength): λ/4 for a single-layered film; λ/2 and λ/4 from the base side for a two-layered film; and λ/4, λ/2, and λ/4 from the base side for a three-layered film.
There is a need for a fluoropolymer antireflective film. The present invention fulfills such need.